java.lang.ClassNotFoundException crash

I got this crash report from many users.

java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.appname/com.unity3d.player.UnityPlayerActivity}: java.lang.ClassNotFoundException: Didn't find class "com.unity3d.player.UnityPlayerActivity" on path: /mnt/asec/com.appname-1/pkg.apk at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2229) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2359) at android.app.ActivityThread.access$700(ActivityThread.java:165) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1326) at android.os.Handler.dispatchMessage(Handler.java:99) at android.os.Looper.loop(Looper.java:176) at android.app.ActivityThread.main(ActivityThread.java:5455) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:525) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1209) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1025) at dalvik.system.NativeStart.main(Native Method) Caused by: java.lang.ClassNotFoundException: Didn't find class "com.unity3d.player.UnityPlayerActivity" on path: /mnt/asec/com.appname-1/pkg.apk at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:64) at java.lang.ClassLoader.loadClass(ClassLoader.java:501) at java.lang.ClassLoader.loadClass(ClassLoader.java:461) at android.app.Instrumentation.newActivity(Instrumentation.java:1078) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2220) ... 11 more

Anyone have any idea what to do???